1. Field of the Invention
The present invention relates in general to reduction gears, and more particularly, to reduction gears of a type which generally comprises a worm and a worm wheel which are operatively engaged and installed in a case. More specifically, the present invention is concerned with reduction gears which are designed to facilitate assembly of parts in a case.
2. Description of the Prior Art
Japanese Utility Model First Provisional Publication 1-143444 shows one conventional reduction gear of the above-mentioned type.
This conventional reduction gear comprises generally a worm to which an input shaft is coaxially fixed, a worm wheel with which the worm is operatively engaged, and a case in which the worm and the worm wheel are installed. The case is formed with an elongate through bore. A generally middle part of the bore constitutes a cylindrical open portion which rotatably and coaxially receives the worm. One end portion of the bore is threaded for detachably receiving a worm bearing bolt. Upon assembly, the worm bearing bolt bears one axial end of the worm to suppress play of the worm.
However, due to its inherent construction, the conventional reduction gear has the following drawbacks.
That is, in order to properly set or assemble the worm in the cylindrical open portion of the bore, the worm should be inserted into the bore from the threaded end portion of the same. Furthermore, this insertion should be made with the worm being rotated about its axis. In fact, because, at the assembly time, the worm wheel is held stationarily in the case, the insertion of the worm into the bore is permitted only when the worm is rotated about its axis in a certain direction. That is, due to rotation of the worm, the external threads of the worm travel in and along the external threads of the worm wheel, which induces the axial movement of the worm in the bore toward the cylindrical open portion. This assembly work is very difficult or at least troublesome.
Furthermore, because the area where the worm bearing bolt bears the worm is not viewed from outside of the case, it is difficult or at least troublesome to obtain a proper bearing of the bolt against the worm.